Why yes, it does take a delicate pedal if I have traction control turned off. Hence my offer to provide video of me losing traction with instantaneous full boost from a 25mph roll.


No 1/4 mile runs or dyno runs on my current setup. No injection.



I have full boost from ~1200RPMS up until redline. Roots blowers are directly proportional to pulley sizes, not RPMS. Let me explain.

The Eaton M90 on the GTP is named so because it moves 90 cubic inches of air for every revolution in "open flow" (not connected to anything). The crank pulley is 7" and the stock supercharger pulley is 3.8". That gives a ratio of 1.84. So at 1,000 engine RPMs the supercharger is doing 1,840 RPMs and at 6,000 engine RPMs the supercharger is doing 11,040 RPMs. So lets calculate how much air is being blown. At 1,000 engine RPMs, 1,840 SC RPMS, the blower pushes 1840 x 90 CI = 165,600 CI .... divide by 1728 to get CFM = 95.83 CFM. At 6000 engine RPMS, 11,040 SC RPMs, the blower pushes 11,040 x 90 CI = 993,600 CI .... divide by 1728 to get CFM = 575 CFM. But wait, that's open flow for the blower. How much can the engine move by itself. Well, the L67 is a 231CI motor, so it would normally move 231CI every two revolutions (every two revolutions because it's a four stroke motor). So, at 1000 engine RPMS, the engine would normally move 231CI x 1000 / 2 = 115,500 CI .... divide by 1728 to get CFM = 66.84 CFM. At 6000 engine RPMs, the engine would normally move 231CI x 6000 / 2 = 693,000CI .... divide by 1728 to get CFM = 401.04CFM.

Ok, now we have what the blower is pushing in CFM and what the engine is pulling in CFM for both 1000 RPM & 6000 RPM. Now to calculate boost at those RPMS. At 1000 RPM the blower is pushing 95.83CFM and the engine is pulling 66.84 CFM. In a perfect world, all 95.83CFM would be crammed into the space of 66.84CFM, resulting in a compression ratio of 95.83/66.84 = 1.433. Standard atmospheric pressure is 14.7 PSI, multiply by 1.433 gives us an absolute pressure of 21.06PSI. Subtract the 14.7 atmospheric to get a boost level of 7.06 PSI. So a stock GTP is running 7 pounds of boost at 1000 RPMs. Now lets look at 6000 RPMs. At 6000 engine RPMs the blower is pushing 575CFM, and the engine is pulling 401CFM. Again, in a perfect world all 575CFM from the blower would be crammed into the 401CFM of the engine, resulting in a compression ratio of 575/401 = 1.433. Wow. Notice the compression ratio is the exact same number. So even at 6000 RPM, the stock GTP is running 7 PSI of boost.

So, as you can plainly see, even a stock gtp has the same boost across it's entire RPM as soon as the bypass valve is closed.

And quickly, checking my own boost levels with a 3.3" supercharger pulley:

7" Crank pulley, 3.3" SC pulley = pulley ratio of 2.12.
2.12 x 90CI x 6000 / 1728 = 662.5 CFM from the blower. We already know that the engine is pulling 401 CFM at 6000 RPM, so 662.5 CFM crammed into 401 CFM gives us a compression ratio of 1.65. Atmospheric PSI of 14.7 x 1.65 = 24.28 Absolute PSI. Subtract the 14.7 PSI Atmospheric to get boost, which gives us 9.58 PSI.

So, in a perfect world a stock gtp is pushing 7 PSI and my modified gtp is pushing 9.58 PSI. But this is not a perfect world. Volumetric Efficiency, heat from compression, friction of the air going through the engine, etc., all make it harder to push the air into the engine. This, in turn, causes the real-world PSI to go up from the theoreticals we see in these calculations. So, in the real-world a stock GTP will see boost levels at about ~8 PSI and I see boost levels at about ~11 PSI.

Another thing to consider is that in the system, it will operate most efficiently at some given RPM, so even though theoretically the boost is flat all the way across, you will see up to 15% difference of boost at different rpms. But, in the roots/screw style supercharger, there is no doubt that full boost, within 15% or so, is available instantaneously.

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Thanks for a real explanation!

So the air the SC is moving vs the air the engine is moving is pretty much the same ratio on your car, thats cool. So a C S/C could do the same but you need a lot more RPMS to get it to move as much air as what the R S/C is moving and thus the full boost in the higher RPMS?

.... and what opens the by pass valve, vacuum? The bypass vents into the atmosphere?

I guess your biggest problem is cooling the intake temps down. Does anyone make a air/air IC with a roots? Maybe off set it to the side and run piping out front and back? Methanol is awesome stuff but sadly it runs out pretty fast.

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2008 Black/Black GXP, purchased 7/23 right off the train.
Mod#1 blacked-out headlights
Mod#2 GMPP Intake -I like to hear my turbo.
Mod#3 Special Sauce
Mod#4 Solo Street Race
'97 Burb.
"07 Charger R/T, Mama's car
Race #1 Charger 0 /Sol 1

Aside from efficiency differences at different RPMS, and position of the bypass, yes. It's actually fairly common for fieros to remove the bypass and run constant boost when the swap in the L67, but from what I gather it's a bit harder on the motor.


Bypass computer controlled, although I think it's PSI/Vacuum operated. When the computer detects throttle acceleration, it closes the bypass valve. The bypass valve doesn't vent anything, it determines if the air is coming into the intake manifold from the supercharger or further up the intake, in effect bypassing the supercharger alltogether. The valve is an integral part of the M90, basically between the SC rotors and the throttle body. So when its open, air flows straight down into the intake, but when its closed, air flows into the rotors first and then down into the intake.


But that does make me wonder what would happen if you could drive a twin screw off of exhaust gasses instead of a belt....

hmmmm....

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That wouldn't make sense; you would need to add some type if a gear reduction to reduce the amount of torque required to turn the blower. The simplicity of a compressor wheel and turbine wheel being connected by a single short shaft would probably out weigh the roots benefits after you added the gear reduction.

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2008 Black/Black GXP, purchased 7/23 right off the train.
Mod#1 blacked-out headlights
Mod#2 GMPP Intake -I like to hear my turbo.
Mod#3 Special Sauce
Mod#4 Solo Street Race
'97 Burb.
"07 Charger R/T, Mama's car
Race #1 Charger 0 /Sol 1

Yep. The problem with roots is the extra 15-20% parasitic loss from the belt, and then the heat from the compression can cause "boost stacking". Which, in a turbo is good effect because it can be matched to a nice power curve and controlled with a boost controller, but on a roots it just causes detonation. In the mildly modded category, it's not that big of a deal. When you get to moderately modified, 12-18PSI, it is absolutely vital to intercool and do mods that reduce backpressure (that's why roots responds well to cams with lots of overlap, and turbos dont!). And of course, when you get to highly modified, over 18+ PSI - you're just much better off going with a twin-screw or turbo.

There are a few home built air/air intercoolers for the M90, but since it's bolted to the intake I haven't been impressed with them. There are plenty of water/air intercoolers, though. Zoomers twincharged has an air/air after the turbo and water/air/after the supercharger - so it's also twincooled.

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The best of both worlds is the variable pitch turbos. There are some prototypes just coming out now that have both adjustable compressor blades and turbine blades. When you add pitch control to the equation the envelope gets that much bigger.

__________________
2008 Black/Black GXP, purchased 7/23 right off the train.
Mod#1 blacked-out headlights
Mod#2 GMPP Intake -I like to hear my turbo.
Mod#3 Special Sauce
Mod#4 Solo Street Race
'97 Burb.
"07 Charger R/T, Mama's car
Race #1 Charger 0 /Sol 1

Oh that does sound tasty! Reminds me of helicopter blades...

Any links?

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Not off hand, there is an editorial in Motor Trend that mentions it briefly. The article is about small displacement motors with turbos to create better mileage.

Variable nozzle turbos:
Honeywell

Variable Vane turbos:
long article
Honeywell again

__________________
2008 Black/Black GXP, purchased 7/23 right off the train.
Mod#1 blacked-out headlights
Mod#2 GMPP Intake -I like to hear my turbo.
Mod#3 Special Sauce
Mod#4 Solo Street Race
'97 Burb.
"07 Charger R/T, Mama's car
Race #1 Charger 0 /Sol 1

The trouble is, you're pulling engine cfm numbers out of your ass from what I see.

If I arbitrarily made up my own numbers I could prove that the earth is going to spiral in to the sun tomorrow.

Then you know nothing about engines.

The eaton M90 is named "M90" because it moves 90 cubic inches of air per rev. The 3800 V6 is a 231 cubic inch, four stroke engine that displaces 231 cubic inches of air every 2 revolutions. The crank pulley and supercharger pulleys on a stock gtp are 7" and 3.8". These are not arbitrary numbers. They are facts. You can look them up if you wish. There are no made up numbers in the calculations above, at all.

Get a clue.

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According to your logic, every engine would make peak horsepower at redline and never have a power "drop off." Why does your nearly 300 ftlb torque V-6 only have 240hp? It's because your engine quickly loses its ability to efficiently move air into the cylinders at high RPM. Engines inherently lose air flow efficiency at certain RPMs(among other things). Apparently, YOU don't have a clue about motors because their pull depends entirely on what the intake, head(s), cam(s) and cam timing allows it.

Oh noez!!1!1 Your numbers are generalities that are more and more wrong with every RPM your engine goes up (past its peak efficiency which is your torque peak, really)... PARTICULARLY with the relatively low RPM tuning of the 3.8. That's right, the 3.8's are tuned to make power relatively at low engine speeds. The cam profile is short in duration and short in lift leading to LOW end torque while sacrificing HIGH end power. How is this relevant to our "discussion?" Low RPM "torque" cams use the short duration and lift to increase air intake velocity. As far as high RPM goes the cylinders are starved for air because there is simply no time nor enough "opening" for it to breath properly. Therefore, your motor will not pull NEARLY as much air as you claim it does.

Lets not get into camshaft timing and how it can further lower your engine CFM at different engine speeds.

One way or another, your idea is flawed and your boost curve varies much more than you say it does.

Perhaps you missed where I already covered all of that.


Race me or STFU newb.


Simple fact of the matter is that you claimed I didn't have PSI in the lower RPM or off of idle, and I have proved that I do.

You got pwnt. Go away.

Don't make me post video.

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post vid anyway!

Here's one:
wheres the turbo lag?

__________________
2008 Black/Black GXP, purchased 7/23 right off the train.
Mod#1 blacked-out headlights
Mod#2 GMPP Intake -I like to hear my turbo.
Mod#3 Special Sauce
Mod#4 Solo Street Race
'97 Burb.
"07 Charger R/T, Mama's car
Race #1 Charger 0 /Sol 1

On the vid, I'll get some this weekend.

On the lag, I don't believe I ever said anything about turbo lag (edit: because I know that turbos can be tuned for anything, and a twin can cover any weak areas). I was just defending the supercharger in the down low. My car responds just like that turbo in that vid.

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